The mechanisms which contribute to the cardiomyopathy observed in the Syrian hamster are being pursued collaboratively in multiple centers using a common animal model. At the Albert Einstein College of Medicine, quantitation of subcellular components during the course of hypertrophy and the development of the myopathy is being explored by electronmicroscopic techniques. The characterization of observed depressions in actomyosin ATPase are being studied to ascertain whether they are due to primary or secondary changes in the composition of the myosin molecule itself. At the Medical College of Virginia, subcellular organelles as well as purified preparations of cell surface membranes are being prepared in order to explore changes which occur in these membranes responsible for mediation of activation and contraction. Initial studies have indicated alteration in composition of both internal and external membranes responsible for transport of calcium and the nature of these changes is being explored using more purified preparations. At the University of Toronto alterations in the metabolism of norepinephrine are being studied and their relation to competency of the nerve endings is being assessed. The switch of metabolism from the synthesis of norepinephrine to the synthesis of dopamine is a unique finding which is also being explored. The changes which occur in histone protein in the nucleus responsible for specific protein synthesis is also being explored in detail. BIBLIOGRAPHIC REFERENCES: Sole, M.J., Lo, C., Laird, C.W., Sonnenblick, E.H. and Wurtman, R.J.: Norepinephrine Turnover in the Heart and Spleen of the Cardiomyopathic Syrian hamster. Circ. Res. 37: 855-862, 1975. Sole, M.J., Lo, C.M., Kamble, A.B., Sonnenblick, E.H., Wurtman, R.J.: Tyrosine Hydroxylase Activity in the Heart and Spleen of the Cardiomyopathic Syrian hamster I. J. Molec. & Cell. Cardiol. (in press) 1976.